Typically, gas turbine engine burners include combustion chambers wherein air compressed by the engine's compressor, is mixed with fuel and the mixture burned, thereby increasing the kinetic energy of the airflow through the engine to produce useful thrust. An ignitor plug which functions similarly to a common spark plug in an automobile engine, provides an electrical spark which initiates the combustion. The ignitor plug typically includes a threaded base which is received within a mating threaded hole in the engine's diffuser case for mounting the plug in the combustion chamber. The ignitor plug extends through a hole in the wall of the combustion chamber such that the tip of the plug where an electric spark is formed, lies in the path of the mixture of fuel and air, providing electrical ignition thereof upon engine start-up.
To maintain the proper alignment of the ignitor plug with the various other combustion chamber components such as the fuel nozzle and various air inlet apertures, as well to aid in the insertion of the plug into the combustion chamber for burner assembly and maintenance, an ignitor plug guide is located in the hole in the combustion chamber wall through which the ignitor plug extends.
It will be appreciated that the environment within a gas turbine engine combustion chamber is extremely harsh. The air fuel mixture burns in the combustion chamber at temperatures as high 2100.degree. C. (3800.degree. F.) causing extreme thermal gradients and therefore, thermal stresses in the combustion chamber walls. Moreover, rotational movement of the engine's fan, compressor and turbine, as well as the high flow rate of the air fuel-mixture and the burning thereof, cause significant vibration in the combustion chamber walls. Such high thermal stresses and vibration experienced by the combustion chamber walls are, of course, also experienced by the ignitor plug guide. Prior art ignitor plug guides have, in large measure, failed to adequately tolerate such a harsh vibratory and thermal environment without themselves exhibiting significant vibratory and even rotational movement. Such movement risks not only the misalignment of the ignitor plug with other components in the combustion chamber such as nozzles, air apertures and the like, but also, actual damage to the barrel of the ignitor plug due to relative vibratory and rotational movement between the plug and the guide.